Still no luck. Adding a drop of Kroil two of three times a day and once a day I give it a crank with the wrenches, but nothing doing other than the crescent slipped and boogered the piston slightly......grrrrr. Keeping after it and will add a torch to the mix tonight.

The crescent wrench is only for the gas block. The gas piston requires a fixed size beefy Craftsman wrench, not some adjustable junk.
I wonder if the rifle was previously owned by a member of the "but I always flush the barrel with hot water after shooting corrosive ammo" fan club. Because in the gas block, that's where the corrosive brine ends up and happily festers while sitting in the safe.

The crescent wrench is only for the gas block. The gas piston requires a fixed size beefy Craftsman wrench, not some adjustable junk.
I wonder if the rifle was previously owned by a member of the "but I always flush the barrel with hot water after shooting corrosive ammo" fan club. Because in the gas block, that's where the corrosive brine ends up and happily festers while sitting in the safe.

Well Mike I know the last time he shot it he didn't as the bore was still filthy ;) I cleaned it first, and thankfully it wasn't surplus ammo, as the bore cleaned up nicely with no pitting, or sign of corrosive ammo. The fellow I got it from said he had not shot it and included an unused shooter's kit, so there is no telling how long the piston has been in place, could even go back to the war. I doubt it, but after something like 10 days of Kroil applications, still no progress. I'm an old, and thus much more patient, man than I once was, so I'll just keep at the slow, but hopefully sure method.

Every step above noted. what size wrench are u using? A small one won't do it. Move a size up or two. Keep the action on the stock for more leverage and hold on with your legs. make sure you place well cover underneath the barrel.

Every step above noted. what size wrench are u using? A small one won't do it. Move a size up or two. Keep the action on the stock for more leverage and hold on with your legs. make sure you place well cover underneath the barrel.

IDK how you get a non-crescent "beefy" wrench? Best I can tell a 9mm is about right as a 3/8's is a tad loose and a 5/16's won't fit. None of them are much bigger than a carpenter's pencil. I'll go to Home Depot and see what options I have tomorrow. IF I leave the action in the stock it sure limits the use of a torch I found out today as the wood is going to get REAL hot in a hurry. I'd have to take out the action, heat it up, and quickly drop it in the stock, add tape to not mar the finish of the gas block and crank away with my new beefy wrench.....nothing's easy.

I removed a stuck gas piston by putting a cork in the muzzle and filling the bore with Kroil until the gas piston was overflowing.I let it set for several days muzzle down.I removed the action from the stock and held the top of the gas block in the padded jaws of a vise.The gas piston on mine did not fit a 9mm wrench.I didn't measure it but appeared to be around 8.5 mm.I used a 8 in crescent wrench to remove the piston.It was very tight.There was no corrosion or gummy lube on the threads.I assume the Germans had a special tool to remove the gas piston.

IDK how you get a non-crescent "beefy" wrench? Best I can tell a 9mm is about right as a 3/8's is a tad loose and a 5/16's won't fit. None of them are much bigger than a carpenter's pencil. I'll go to Home Depot and see what options I have tomorrow. IF I leave the action in the stock it sure limits the use of a torch I found out today as the wood is going to get REAL hot in a hurry. I'd have to take out the action, heat it up, and quickly drop it in the stock, add tape to not mar the finish of the gas block and crank away with my new beefy wrench.....nothing's easy.

Don't not use a torch. Milwaukee makes an adjustable temp heat gun that I've used for these types of problems. Make sure you take the action OUT of the stock before you heat it up.